Finned heat exchanger coil assemblies are widely used in a number of applications in fields such as air conditioning and refrigeration. A finned heat exchanger coil assembly generally includes a plurality of spaced parallel tubes through which a heat transfer fluid such as water or refrigerant flows. A second heat transfer fluid, usually air, is directed across the tubes. A plurality of fins is usually employed to improve the heat transfer capabilities of the heat exchanger coil assembly. Each fin is a thin metal plate, made of copper or aluminum, which may or may not include a hydrophilic coating. Each fin also acts as a tubesheet and includes a plurality of apertures for receiving the spaced parallel tubes, such that the tubes generally pass through the plurality of fins at right angles to the fins. The fins are arranged in a parallel, closely spaced relationship to one another along the tubes to form multiple paths for the air or other heat transfer fluid to flow across the fins and around the tubes.
In heat exchanger coil assemblies, it is desirable to maximize the amount of heat transfer within a given coil. Once way to increase heat transfer is to increase the size of the fin. However, increasing the size of the fin leads to a larger device and to a higher, air-side pressure drop, both of which are undesirable. “Pressure Drop” is the air pressure difference required to maintain air flow through the heat exchanger coil assembly. High pressure drop is undesirable since the energy required to keep air flowing through the coil assembly is proportional to the pressure drop across the coil assembly. Higher coil pressure drop leads to higher energy (typically electrical) usage, for a given building HVAC system.
In a heat exchanger coil assembly for dehumidifying air, relatively warm and humid air flows into the coil, and as the air becomes cooler, it becomes saturated with water. At some point, the cooled air reaches its dew point and is unable to hold moisture as it is cooled further, resulting in condensation on the fin plate. The resulting condensate on the fin inhibits heat transfer between the fin and the air. The condensate is typically removed from the fin plate by one of two mechanisms. The first mechanism is gravity-induced drainage along the fin surface into a pan located under the coil assembly. This mechanism of condensate removal is desirable, and results in plate fins being oriented vertically in dehumidification coils. The second mechanism for condensate removal is entrainment of condensate droplets by the airflow exiting the coil. This mechanism of condensate removal is typically undesirable, since it can lead to problematic biologic activity on downstream surfaces of the equipment housing the coil assembly. Thus, it is desirable to provide the fin with a structure that minimizes the condensate inventory residing on the fin surface, facilitates and maximizes gravity-induced drainage of condensate from the coil assembly, and inhibits entrainment of condensate droplets into the exiting airflow. To solve these problems, some fins are produced or manufactured having complex geometries which are difficult and expensive to manufacture.
Therefore, what is needed is a fin geometry that is simple and inexpensive to manufacture while maximizing the heat transfer capabilities of the fin. In addition, a fin geometry is needed that can remove moisture from the air passing over the fin and reduce the amount of condensation that is permitted to reside on the fins.